Base station apparatus and termnal apparatus

ABSTRACT

A base station apparatus corresponding to a first base station apparatus of base station apparatuses and connected to terminal apparatuses, first base station apparatus transmitting and receiving first packets with respect to a second base station apparatus corresponding to another of base station apparatuses and transmitting and receiving second packets with respect to terminal apparatuses, first base station apparatus transmits a third packet to second base station apparatus, third packet corresponding to one of first packets to be transmitted from first base station apparatus and including a first data item, second base station apparatus recognizing by first data item that first base station apparatus is one of base station apparatuses, third packet being used through an authentication process or an association process for connecting in wireless first base station apparatus to second base station apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/172,946, filed Jul. 5, 2005, which is a continuation of Ser. No.10/242,632, filed Sep. 13, 2002, which is based upon and claims thebenefit of priority from Japanese Patent Application No. 2001-304700,filed Sep. 28, 2001, the entire contents of each of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication system which iscomprised by a plurality of base stations and a plurality of terminals,each of the terminals being connected to one of the base stations. Morespecifically, the invention relates to techniques for connecting basestations wirelessly, without being influenced by a communication betweena base station and a terminal, and without influencing it.

2. Description of the Background

As a wireless LAN, a wireless LAN system based on IEEE802.11(ISO/IEC8802-11:1999(E) ANSI/IEEE Std 802.11, 1999 edition) is known. Asone form of such wireless LAN system, an element called a Basic ServiceSet (BSS) in which a base station covers a plurality of terminals isused, and a plurality of BSSs form a network. A structural element thatconnects neighboring BSSs is called a Distribution System (DS). A basestation establishes (sets) connection to this DS, and packets aretransmitted between the BSS and DS via the base station. The entirenetwork extended by the DS is called an ESS (Extended Service Set). Inthe IEEE802.11 wireless LAN system, a description about implementationof the DS is not specified.

Communications between base stations are also used in a cellular phonesystem when a terminal connected to a given base station transmits datato a terminal connected to another base station.

The conventional wireless LAN system suffers the following problems.

(1) A practical protocol upon connecting base stations via a wirelesscommunication is not established.

(2) Since a plurality of terminals are connected to a base station, poorreliability of communications between base stations seriously influencesthe entire system.

(3) Wireless resources are spent for communications between basestations and, in particular, in a system in which base stations andterminals are connected via wireless communications, the communicationcapacity within the area covered by each base station decreases.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a base stationapparatus which can connect wirelessly to another base stationefficiently, and can communicate with the another base station withoutbeing influenced by a communication between the base station andterminals, and without influencing it.

It is another object of the present invention to provide a terminalapparatus which can communicate efficiently with the base station whichcan communicate with other base stations.

According to a first aspect of the present invention, there is provideda base station apparatus corresponding to a first base station apparatusof a plurality of base station apparatuses and connected to a pluralityof terminal apparatuses, the first base station apparatus transmittingand receiving a plurality of first packets with respect to a second basestation apparatus corresponding to another of the base stationapparatuses and transmitting and receiving a plurality of second packetswith respect to the terminal apparatuses, the first base stationapparatus comprises: a transmitter unit configured to transmit a thirdpacket to a second base station apparatus, the third packetcorresponding to one of the first packets to be transmitted from thefirst base station apparatus and including a first data item, the secondbase station apparatus recognizing by the first data item that the firstbase station apparatus is one of the base station apparatuses, the thirdpacket being used through an authentication process or an associationprocess for connecting in wireless the first base station apparatus tothe second base station apparatus.

According to a second aspect of the present invention, there is provideda base station apparatus corresponding to a first base station apparatusof a plurality of base station apparatuses and connected to a pluralityof terminal apparatuses, the first base station apparatus transmittingand receiving a plurality of packets with respect to a second basestation apparatus corresponding to another of the base stationapparatuses, the second base station apparatus broadcastingsynchronization signals, the first base station apparatus comprises: asynchronization unit configured to synchronize a transmission timing ofthe first base station apparatus for transmitting the packets with thatof a second base station apparatus, based on the synchronization signalsbroadcasted by the second base station apparatus; and a transmitter unitconfigured to transmit a first packet to the second base stationapparatus in the transmission timing of the first base station apparatussynchronized with that of the second base station apparatus, the firstpacket corresponding to one of the packets to be transmitted from thefirst base station and including a first data item, the second basestation apparatus recognizing by the first data item that the first basestation apparatus is one of the base station apparatuses, the firstpacket being used through an authentication process or an associationprocess for connecting in wireless the first base station apparatus tothe second base station apparatus.

According to a third aspect of the present invention, there is provideda terminal apparatus corresponding to a first terminal apparatus of aplurality of terminal apparatuses and connected to a base stationapparatus, the first terminal apparatus transmitting and receiving aplurality of packets with respect to the base station apparatus and theterminal apparatuses other than the first terminal apparatus, a firstterminal apparatus comprises: a receiver unit configured to receive afirst packet which corresponds to a packet which is not addressed to thefirst terminal apparatus; and, a transmission control unit configured tocontrol an operation for transmitting the packets from the firstterminal apparatus, when the first packet satisfies a predeterminedcondition, and configured not to control the operation when the firstpacket does not satisfy the condition, the condition being that thefirst packet is transmitted and is to be received among the base stationapparatus and the terminal apparatuses other than the first terminalapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of the overall arrangement of a wireless LANsystem according to the first embodiment of the present invention;

FIG. 2 shows an example of the overall arrangement of another wirelessLAN system according to the first embodiment of the present invention;

FIG. 3 is a functional block diagram of a base station apparatus;

FIG. 4 is a functional block diagram of a terminal apparatus;

FIG. 5 is a chart for explaining a procedure until base stations AP1 andAP2 recognize each other's partners as base stations upon makingcommunications between them;

FIG. 6 is a view for explaining a MAC frame specified by IEEE802.11;

FIG. 7A shows an example of an address table of the base station AP1;

FIG. 7B shows an example of an address table of the base station AP2;

FIG. 8A shows an example of system configuration for explaining NLOS(Non Line of Sight) communications;

FIG. 8B shows an example of system configuration for explaining LOS(Line of Sight) communications;

FIG. 9 is a view for explaining a method of using the address field ofthe MAC frame;

FIG. 10 shows a sequence for explaining the procedure of wirelesscommunications via two base stations;

FIGS. 11A and 11B are flow charts for explaining processes uponreceiving a data frame in a base station and terminal;

FIG. 12 is a diagram showing an example of the arrangement of principalpart of a wireless LAN system according to the third embodiment of thepresent invention;

FIG. 13 is a block diagram showing an example of the arrangement of adirectional antenna 2;

FIG. 14 is a flow chart for explaining a procedure until base stationsAP1 and AP2 recognize each other's partners as base stations upon makingcommunications between them;

FIG. 15 is a diagram showing an example of the arrangement of principalpart of a wireless LAN system according to the fourth embodiment of thepresent invention;

FIG. 16 is a block diagram showing an example of the arrangement of abase station apparatus;

FIG. 17 is a block diagram showing an example of the arrangement of anadaptive array antenna;

FIG. 18 is a block diagram showing an example of the arrangement ofprincipal part of a base station apparatus that makes transmitter powercontrol;

FIG. 19 is a flow chart for explaining the processing operation of thebase station apparatus;

FIG. 20 is a chart for explaining the transmitter power controlprocedure upon exchanging data between base stations;

FIG. 21 is a flow chart for explaining the transmitter power controlprocedure of the base station;

FIG. 22 is a chart for explaining the transmitter power controlprocedure upon exchanging data between base stations in case of makingshared key authentication;

FIG. 23 is a chart for explaining the transmitter power controlprocedure upon exchanging data between base stations in case of makingtransmitter power control in association;

FIG. 24 is a block diagram showing an example of the arrangement of abase station apparatus that controls the carrier sense level; and

FIG. 25 is a flow chart for explaining the carrier sense level controlprocedure of the base station apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be describedhereinafter with reference to the accompanying drawings.

In the present invention, an IEEE802.11 wireless LAN system will beexemplified. However, the present invention is not limited to theIEEE802.11 wireless LAN system, but may be applied to other wireless LANsystems, wireless MAN (Metropolitan Area Network) systems of, e.g., FWA(Fixed Wireless Access), and BWA (Broadband Wireless Access) systems.

The communication system according to embodiments to be describedhereinafter can be applied to a communication system which is comprisedby a plurality of base stations and a plurality of terminals, the basestations inter-connecting wirelessly, each of the terminals connectingto one of the base stations either through wire or wirelessly. When agiven base station connects to another base station wirelessly andconnects to a terminal through wire, such base station must have a firstcommunication unit used to communicate wirelessly with the another basestation, and a second communication unit used to communicate with theterminal through wire.

In such communication system, the embodiments to be describedhereinafter can be applied to a case wherein a base station connectswirelessly to another base station, and a case wherein a terminalconnecting wirelessly to a base station communicates with the basestation, and the like.

First Embodiment

The procedure until two base stations recognize each other's partners asbase stations when one of the two base stations connects to the other,will be explained below.

FIG. 1 illustrates the arrangement of an ESS (Extended Service Set)formed by two BSSs (first and second BSSs) in an IEEE802.11 wireless LANsystem.

The first BSS includes a base station AP1 serving as an access point,and a plurality of (e.g., two in this case) wireless terminals (to besimply referred to as terminals hereinafter) STA11 and STA12 connectedto the base station AP1. Each of the terminals serves as a station in anIEEE802.111 wireless LAN system. The second BSS includes a base stationAP2 serving as an access point, and a plurality of (e.g., two in thiscase) wireless terminals (to be simply referred to as terminalshereinafter) STA21 and STA22 connected to the base station AP2.

As shown in FIG. 1, the base station (e.g., AP1) may be connected to awired network 5.

FIG. 3 shows an example of the arrangement of principal part of the basestations AP1 and AP2. In the following description, when the basestations AP1 and AP2 need not be distinguished from each other (in caseof an explanation common to the two base stations), they will be simplyreferred to as a base station AP.

In FIG. 3, a receiver ii receives a signal (corresponding to a packet)transmitted from a terminal or another base station via an antenna 20,and generates a received signal via processes including demodulation anddecoding. A transmitter 12 generates a signal (corresponding to apacket) to be transmitted to a terminal or another base station via theantenna 20, and supplies such signal to the antenna 20.

A packet received as the received signal by the receiver 11 is input toa receiving control unit 13, which executes a predetermined receivingprocess and the like that comply with IEEE802.11 (including IEEE802.11aand IEEE802.11b).

A transmitting control unit 14 executes a predetermined transmittingprocess and the like that include generation of packets to bebroadcasted or subjected to a unicast to a terminal or another basestation, and comply with IEEE802.11 (including IEEE802.11a andIEEE802.11b). A packet generated by the transmitting control unit 14 istransmitted to a terminal or another base station as a transmittingsignal via the transmitter 12. An address table 21 and timer 22 will beexplained later.

FIG. 4 schematically shows an example of the arrangement of principalpart of the terminals STA11, STA12, STA21, and STA22. In the followingdescription, when the terminals STA11, STA12, STA21, and STA22 need notbe distinguished from each other (in case of an explanation common toall the terminals), they will be simply referred to as a terminals STAsand one of the terminals STA11, STA12, STA21, and STA22 will be simplyreferred to as a terminal STA.

The terminal STA comprises at least an antenna 200, receiving unit 201,transmitting unit 207, data processing unit 208, and timer 210.

For example, when a data to be transmitted as a packet is generated or atransmission instruction of a packet is issued by user's operation (atransmission request is generated), the data processing unit 208 passesthe packet to the transmitting unit 207 in response to that request. Thetransmitting unit 207 converts the packet (e.g., an IP packet) into aMAC frame specified by IEEE802.11. The MAC frame as digital data isconverted into a radio signal of a predetermined frequency (e.g., 2.4GHz), and the radio signal is transmitted from the antenna 200 as aradio wave.

On the other hand, the receiving unit 201 converts a signal received bythe antenna 200 into a MAC frame as digital data, extracts received data(packet) from an information field in this MAC frame, and passes thatdata to the data processing unit 208. In this case, the data processingunit 208 executes a process for, e.g., displaying the received data on adisplay. Note that the data processing unit 208 may execute variousother data processes.

The timer 210 is used for a TSF (Timing Synchronization Function)specified by IEEE802.11 (including IEEE802.11a and IEEE802.11b). Thetimer (TSF timer) 210 will be described later.

A case will be explained below wherein the base station AP2 accesses thebase station AP1 in the arrangement shown in FIG. 1. Assume that thebase station AP1 does not know (recognize) the presence of the basestation AP2. Even in this case, the base station AP2 can receive abeacon frame which is transmitted from the base station AP1 andspecified by IEEE802.11 (including IEEE802.11a and IEEE802.11b).

FIG. 5 is a flow chart for explaining the procedure until the basestations AP1 and AP2 recognize each other's partners as base stationswhen the base station AP2 connects to the base station AP1. Thefollowing explanation will be given with reference to this flow chart.

According to the specifications of IEEE802.11 (including IEEE802.11a andIEEE802.11b), all terminals connected to a given base station aresynchronized with the timer 22 of that base station in a BSS. That is,the base station has the timer (TSF (Timing Synchronization Function)timer) 22, and periodically transmits a beacon frame including the timervalue to a terminal connecting to that base station. Upon receiving thebeacon frame, the terminal adjusts its own timer (TSF timer) 210 to thetimer value in a timestamp field contained in the beacon frame, thussynchronizing with the base station. Since the beacon frame has suchfunction, it is also called a synchronization signal.

A case will be described below wherein the base station AP2 adjusts(synchronizes) the timer value of its own timer 22 to the timer 22 ofthe base station AP1 and then connecting to the base station AP1.

As shown in FIG. 5, the base station AP2 receives a beacon frameperiodically transmitted from the base station AP1 (step S301)

According to the specifications of IEEE802.11 (including IEEE802.11a andIEEE802.11b), since the timestamp field of the received beacon frame iswritten with a copy (timestamp value) of the timer value of the timer 22of the base station AP1, the base station AP2 sets the receivedtimestamp value in its timer 22 (step S302).

The base station AP2 starts a procedure for making the base station AP1recognize that the self station AP2 is a base station.

According to the specifications of IEEE802.11 (including IEEE802.11a andIEEE802.11b), authentication and association processes follow. In thisembodiment, a data item which informs the base station AP1 that the basestation AP2 is a base station is written in at least one of the framesused in authentication and association processes.

The MAC frame specified by IEEE802.11 is formed of a MAC header of themaximum of 30 bytes, which stores various kinds of control information,a data field that stores data at the maximum of 2312 bytes, and a framecheck sequence (FCS) used to check if data are transmitted normally, asshown in FIG. 6.

The MAC frame includes three types of frames, i.e., a management framesuch as an authentication frame, an association frame, or the like, acontrol frame used in access control such as an ACK (Acknowledgement)frame, an RTS (Request to Send) frame, aCTS (Clear to Send) frame, orthe like, and a data frame for data communications. The type of each ofthese three MAC frames is indicated by “type” in a frame control fieldin the MAC header. Furthermore, “subtype” in the frame control fieldindicates the detailed type of a MAC frame such as beacon,authentication, association, ACK, RTS (Request to Send), CTS (Clear toSend), and the like.

The frame control field contains a “To DS” field (1 bit) and a “From DS”field (1 bit). These fields are used in a data frame, but are not usedin other types of frames (e.g., authentication and association frames)since “0” is always written in these fields. In this embodiment, uponauthentication (or association), the base station AP2 writes “1” in bothof the “To DS” and “From DS” fields and transmits that frame to the basestation AP1 upon the frame format shown in FIG. 6 to the base stationAP1.

In FIG. 5, a frame with “To DS” and “From DS” fields=“1” is transmittedupon authentication. In this case, the transmitting control unit 14 ofthe base station must additionally have a processing function ofrewriting the contents of the “To DS” and “From DS” fields by “1” in aframe to be transmitted upon executing a process corresponding toauthentication with the base station as a partner. On the other hand,the receiving control unit 13 of the base station must additionally havea processing function of checking the “To DS” and “From 'OS” fields inthe received frame upon executing a process corresponding toauthentication with the base station as a partner.

The base station AP2 transmits, to the base station AP1, a frame thatrequests authentication and is specified by IEEE802.11 (includingIEEE802.11a and IEEE802.11b) (an authentication frame withauthentication transaction sequence number (to be simply referred to asATSN hereinafter)=1) (step S303). In this frame, the “To DS” and “FromDS” fields are “1”. Upon receiving this frame, since the “To DS” and“From DS” fields are “1”, the base station AP1 transmits anauthentication frame (ATSN=2) specified by IEEE802.11 (includingIEEE802.11a and IEEE802.11b) to the base station AP2 under theassumption that the source of the received frame is a base station (stepS304). The “To DS” and “From DS” fields in this frame are “1”.

If authentication has succeeded, the base station AP2 then transmits anassociation request frame specified by IEEE802.11 (including IEEE802.11aand IEEE802.11b) to the base station AP1 (step S305) Upon receiving thisframe, the base station AP1 transmits an association response framespecified by IEEE802.11 (including IEEE812.11a and IEEE802.11b) to thebase station AP2 (step S306). If association has succeeded, the basestation AP recognizes the base station AP2 as a base station (stepS307).

Upon association, a frame with “To DS” and “From DS”=“1” may betransmitted.

According the specifications of IEEE802.11 (including IEEE802.11a andIEEES02.11b), a “capability information” field is inserted in such asassociation request, beacon, probe response frames, but a portion usedto describe ESS and IBSS in a “capability information” field is usedonly in case of a beacon frame and a probe response frame. Hence, theinformation (the data item) that informs the base station AP1 that thebase station AP2 is a base station may be written in this portion uponassociation. Also in this case, the base station AP1 can similarlyrecognize the base station AP2 as a base station as described above.

With the procedure described so far, the base station AP1 recognizes thebase station AP2 as a base station.

For the purpose of relaying a frame from a first terminal in one BSS toa second terminal in the other BSS in a DS communication, each of thebase stations may have an address table 21 that registers the addresses(e.g., MAC addresses) of terminals connected to each of the basestation.

As shown in FIGS. 7A and 7B, the address table 21 registers theaddresses (e.g., MAC addresses) of terminals connected to a given basestation in correspondence with the address (e.g., MAC address) of thatbase station serving as a relay apparatus. For example, FIG. 7A shows anaddress table corresponding to the first BSS to which the base stationAP1 belongs, and FIG. 7B shows an address table corresponding to thesecond BSS to which the base station AP2 belongs.

In the following description, the addresses (MAC addresses) of the basestations AP1 and AP2 are “AP1” and “AP2” respectively, using theirreference symbols without change, and the addresses (MAC addresses) ofthe terminals STA11, STA12, STA21, and STA22 are “STA11”, “STA12”,“STA21”, and “STA22” respectively, using their reference symbols withoutchange. Also, the addresses (MAC addresses) of the base stations areused as identifiers (BSSID) of the BSSs to which the base stationsbelong.

At the time of completion of step S307 in FIG. 5, the base station AP1has not acquired information (e.g., the address table shown in FIG. 7B)indicating terminals connected to the base station AP2 yet. Also, thebase station AP2 has not acquired information (e.g., the address tableshown in FIG. 7A) indicating terminals connected to the base station AP1yet. Hence, the base stations AP1 and AP2 exchange their address tableswith each other (step S308). As a result, the base station AP1 canacquire the address table shown in FIG. 7B in addition to that shown inFIG. 7A (step S309). Also, the base station AP2 acquires the addresstable shown in FIG. 7A in addition to that shown in FIG. 7B (step S309).

In this manner, since each base station has an address table of otherbase stations with which that base station can easily relay a dataframe. That is, if a data frame received by a base station is addressedto a BSS other than that to which the self station belongs, the basestation looks up the address table to determine a BSS and next basestation to which that data frame is to be transmitted, and can transmitthe data frame to the next base station.

The base stations AP1 and AP2 need not hold such address tables 21 bythemselves. For example, as shown in FIG. 2, a management apparatus 100that manages the address tables of all base stations together may beadded, and may be connected to each of the base stations AP1 and AP2. Inthis case, the base station AP2 registers the address table (FIG. 7B)corresponding to the BSS of the self station in the management apparatus100 in step S308 in FIG. 5. The base station may access the managementapparatus 100 when it must look up the address table.

In a small-scale system, each base station may hold only the addresstable corresponding to the BSS of the self station, but need not holdthat of another base station. In such case, when a data frame receivedby a base station in the system is addressed to a terminal of a BSSother than that to which the self station belongs, the base station maytransmit the data frame to all other base stations.

In this manner, the base station AP2 is recognized by the base stationAP1 as a base station and setup connection with the base station AP1,and can realize a DS communication with the base station AP1. At thesame time, the base station AP2 can communicate with terminals in thesecond BSS of the self station. That is, the base station AP2 begins tooutput a beacon frame.

A terminal (e.g., STA21) in the second BSS receives a beacon frametransmitted from the base station AP2, and can then communicate with thebase station AP2 and another terminal (e.g., STA22) in the second BSS.Also, a terminal (e.g., STA21) in the second BSS can communicate withthe base station AP1 which belongs to the first BSS, via the basestation AP2. Furthermore, a terminal (e.g., STA21) in the second BSS cancommunicate with a terminal (e.g., STA21) which belongs to the firstBSS, via the base station AP1. Moreover, a terminal (e.g., STA21) in thesecond BSS can communicate with a terminal on the wired network via thebase station AP1.

As described above, according to the first embodiment, wirelesscommunication connection between base stations can be established, theDS can be easily formed and, hence, a new base station can be easilyadded. Since a new base station can be easily added as needed, promptactions can be taken on broadening a communication area, and animprovement of communication quality with terminals in a very badwireless communication environment.

Merits obtained upon adding a new base station will be described belowwith reference to FIG. 8A and FIG. 8B.

FIG. 8A shows a case wherein terminals STA501 to STA503 are present in ameeting room on the other side of a wall or the like from a base stationAP1. In this case, communications between the base station AP1 andterminals STA501 to STA503 become NLOS (Non Line of Sight)communications due to the presence of the wall, resulting in a poorcommunication condition. Hence, a base station AP2 as a new base stationis located at a position where it can easily communicate with the basestation AP1 and the terminals STA501 to STA503, i.e., at a positionwhere LOS (Line Of Sight) communications with the terminals STA501 toSTA503 can be assured, as shown in FIG. 8B.

The base stations AP1 and AP2 are connected wirelessly, and theterminals STA501 to STA503 are connected to the base station AP2wirelessly. Since the communication between the base station AP1 and theterminals STA501 to STA503 is established by way of the base station AP2as a relay point, faster, higher quality communications can be achievedcompared to the arrangement shown in FIG. 8A.

In this way, a base station can be added not only in the wireless LANsystem but also in a system of FWA and the like.

In the first embodiment, the timers 22 of the base stations AP2 and AP1are synchronized (the two base stations transmit frames such as beaconframes and the like at nearly the same timing). Hence, the first andsecond BSSs can be synchronized, and a hidden-terminal problem betweenBSSs can be avoided. That is, the probability of collision upontransmitting frames between terminals, which can receive signals in thefirst and second BSS5, can be avoided by the NAV (Network AllocationVector) specified by IEEE802.11 (including IEEE802.11a and IEEE802.11b).According to the first embodiment, interference can be eliminated, andthe communication quality in respective BSSs can be improved.

Since the timers 22 of the base stations AP2 and AP1 are synchronized,these base stations transmit beacon frames at nearly the same timing.Therefore, upon transmitting a beacon frame from the base station AP2, abeacon frame from the base station AP1 cannot often be received since itis transmitted at the same timing.

Hence, after the transmitting control unit 14 of the base station AP2transmits a beacon frame a predetermined number of times, it may stoptransmission of beacon frame, and receive a beacon frame transmittedfrom the base station AP1, to check if the transmission timing of thebeacon frame is synchronized with that of the base station AP1. Andtransmission timing of beacon frames may be adjusted.

Or, when the base station AP2 does not receive any beacon frame from thebase station AP1 in a receiving phase, it may be determined that thebeacon frame transmission timing is synchronized with that of the basestation AP1. On the other hand, when the base station AP2 receives abeacon frame from the base station AP1 in a receiving phase, it mayadjust the beacon frame transmission timing of the self station to thatof the base station AP1.

Furthermore, when the base stations AP1 and AP2 transmit beacon framesusing different channels, the base station AP2 may have another receiverunit for the channel that the base station AP1 uses to transmit a beaconframe. In this case, the base station AP2 can receive a beacon framefrom the base station AP1 even while it transmits a beacon frame, thusadjusting the beacon frame transmission timing to that of the basestation AP1.

Second Embodiment

In the first embodiment, the base station AP2 adjusts (synchronizes) thetimer value of its timer 22 to that of the base station AP1, and thenaccess the base station AP1 (step S302 in FIG. 5). However, the presentinvention is not limited to such specific case, and the base station AP2may operate asynchronously with the base station AP1. That is, theprocess in step S302 in FIG. 5 (i.e., the process for adjusting thetimer value of the timer 22 of the self station to that of the basestation AP1 on the basis of a beacon frame transmitted from the basestation AP1) may be omitted.

In case that the base stations AP1 and AP2 operate whether synchronouslyor asynchronously, when the base station AP1 (AP2) receives frames whichare exchanged within the first BSS (the second BSS) to which the basestation AP1 (AP2) belongs, the base station AP1 (AP2) sets atransmission wait time (sets NAV) to avoid collision.

In case that the base stations AP1 and AP2 operate asynchronously, theytransmit beacon frames at different timing. In this case, the basestation AP2 receives not only frames which are exchanged within thefirst BSS to which the base station AP1 belongs, but also beacon framesfrom the base station AP1. According to the prior art, the base stationAP2 sets the NAV, when it receives frames which are exchanged within thefirst BSS and the beacon frames from the base station AP1 to avoidcollision with them. For this reason, communications between the basestation AP2 and the base station AP1 and those in the second BSS areextremely suppressed. The same applies to the base station AP1.

To solve such a problem, the base station AP may deliberately permitradio wave collision, and give priority to communications between basestations over those in the BSS to which the self station belongs.

Upon receiving a frame, the base station according to the secondembodiment checks the address field of the frame, and (a1) the basestation executes a predetermined receiving process, when the receivedframe is a frame transmitted to the self station from another BSSdifferent from the BSS to which the self station belongs or a framewhose destination or source is a terminal in the BSS of the selfstation, (a2) the base station makes an operation for suppressingtransmission of frames from the self station (sets the NAV), when thereceived frame is a frame which is used in communications betweenterminals in the BSS to which the self station belongs without beingrelayed by the self station, furthermore, (a3) the base station discardsthe received frame without processing it (without setting any NAV), whenthe received frame is a frame which is used for communicating only inanother BSS different from the BSS to which the self station belongs.

In case of (a3), since no NAV is set, when the base station AP2 (or AP1)has a frame to be transmitted to the other base station AP1 (or AP2),the base station AP2 (or AP1) can quickly start transmission to theother base station AP1 (or AP2).

And when the base station AP2 (or AP1) has a frame to be transmitted toa terminal in a BSS to which the self station belongs, if nocommunications are made in the BSS, the base station can quickly starttransmission to that terminal.

When a given terminal can receive frames in the first and second BSSs,according to the prior art, the terminal suppresses the transmission offrame by the NAV when the terminal receives a frame other than a framewhich is addressed to the self apparatus.

Hence, upon receiving a frame, a terminal according to the secondembodiment checks the address field of the received frame, and (b1) theterminal executes a predetermined receiving process, when the receivedframe is addressed to the self apparatus, (b2) the terminal makes anoperation for suppressing transmission of frames from the self apparatus(sets the NAV), when the received frame is a frame which is transmittedto or from any one of the terminals or a base station in the BSS towhich the self apparatus belongs (i.e. when the received frame containsthe address (like “BSSID”) of the base station of the BSS to which theself apparatus belongs), (b3) the terminal discards the received framewithout processing it (without setting any NAV), when the address (like“BSSID”) of the base station of the BSS to which the self apparatusbelongs is not contained the received frame.

In this manner, since each terminal according to the second embodimentdoes not set any NAV when it receives a frame which does not contain theaddress (like “BSSID”) of the base station of the BSS to which the selfapparatus belongs, if there is a frame to be transmitted, the terminalcan efficiently start transmission without any transmission wait time.

Such processes for the received frame in the base station AP andterminal STA are applied not only to a case wherein the base stationsAP1 and AP2 operate asynchronously, but are applied to a case whereinthe base stations AP1 and AP2 operate synchronously as in the firstembodiment, so as to make efficient communications.

The aforementioned processes for the received frame in the base stationAP and terminal STA can be implemented by checking four address fields(“address 1”, “address 2”, “address 3”, “address 4”), and the “To DS”and “From DS” fields in the control field in the MAC frame shown in FIG.6.

How to use respective fields specified by IEEE802.11 (includingIEEE802.11a and IEEE802.11b) will be briefly explained below.

The “To DS” field is used in a data frame. When a frame is transmittedto the base station in DS communications, “1” is set in this field;otherwise, “0” is set.

The “From DS” field is used in a data frame. When a frame is transmittedfrom the base station in DS communications, “1” is set in this field;otherwise, “0” is set.

A data frame in which both the “To DS” and “From DS” fields are “0”, theframe is a data frame which is transmitted from one terminal to anotherterminal in one BSS. A data frame in which the “To DS” field is “1” andthe “From DS” field is “0”, is a data frame transmitted from a giventerminal to a base station though a DS communication. A data frame inwhich the “To DS” field is “0” and the “From DS” field is “1”, is a dataframe transmitted from a given base station to a terminal through a DScommunication. A data frame in which both the “To DS” and “From DS”fields are “1”, is a data frame transmitted from a given base station toanother base station through a DS communication.

The four address fields respectively contain one of the BSSID (basicservice set identifier), source address (SA), destination address (DA),transmitter address (TA), and receiver address (RA).

The BSSID indicates a BSS where the source of the frame is present.Normally, the BSSID is the MAC address of the base station.

The DA indicates the MAC address of a destination that finally receivesthe frame.

The SA indicates the MAC address of the source that generated the frame.

The TA indicates the MAC address of a source which received andtransmitted the frame as a relay point for transmitting the frame to theDA.

The RA indicates the MAC address of a destination which receives theframe as a relay point for transmitting the frame to the DA.

The method of using the four address fields and “To DS” and “From DS”fields will be described below with reference to FIG. 9 taking as anexample a case wherein a frame is to be transmitted from the terminalSTA21 to the terminal STA11.

Assume that the base station AP2 is recognized as a base station by thebase station AP1 via the procedure shown in FIG. 5.

As shown in FIG. 10, the terminal STA21 receives a beacon frametransmitted from the base station AP2 (step S351), and executesauthentication and association (steps S352 and S353). If authenticationand association have succeeded, the terminal STA21 transmits a dataframe addressed to the terminal STA11.

In such case, the terminal STA21 transmits the data frame to the basestation AP2 (step S354) The uppermost column of FIG. 9 shows thecontents of the four address fields and “To DS” and “From DS” fields inthe data frame at step S354.

The base station AP2 then transmits the data frame to the base stationAP1 (step S355). The second uppermost column of FIG. 9 shows thecontents of the four address fields and “To DS” and “From DS” fields inthe data frame at step S355.

Furthermore, the base station AP1 transmits the data frame to theterminal STA11 (step S356). The third uppermost column of FIG. 9 showsthe contents of the four address fields and “To DS” and “From DS” fieldsin the data frame at step S356.

The processing operation upon receiving a data frame in the terminal STAand base station AP will be described below with reference to FIGS. 11Aand 11B. Note that, upon exchanging a data frame in FIGS. 11A and 11B,an RTS/CTS frame may be exchanged in advance, and an ACK frame istransmitted from the receiving side of a unicast data frame.

Note that the conventional operation is indicated by the dotted line inFIGS. 11A and 11B, for clarifying differences between the conventionalsystem and the system according to the second embodiment.

The receiving processing operation of a data frame in the base stationAP will be explained first. The base station AP receives a frame (stepS401). If the received frame is a frame which addressed to the selfstation, in which the address of the self station is described as “DA”,“RA”, or “BSSID” (i.e. the received frame is a frame which istransmitted from another BSS different from the BSS to which the selfstation belongs to, or a frame whose destination or source is a terminalin the BSS of the self station) (step S411), the base station APexecutes a receiving process corresponding to the received frame (stepS412).

If the received frame is a data frame that is used in communicationsbetween terminals in the BSS to which the self station belongs (forexample a data frame that is used in communications between terminals inthe BSS to which the self station belongs without being relayed by theself station) (step S413), the flow advances to step S414, and the basestation AP makes an operation for suppressing transmission of a dataframe from the self station (sets the NAV).

If it is determined in step S413 that the received frame is a data framewhich is used for communicating in another BSS different from the BSS towhich the self station belongs, the flow advances to step S415, and thebase station AP discards the frame (without setting any NAV, althoughthe NAV is set in such case in the conventional system).

More specifically, as shown in FIG. 11A, if the address of the selfstation is stored in the “address 1” field of the received frame in stepS411, the base station executes a predetermined receiving process forthe received frame (step S412).

In step S413, when the “From DS” field of the received frame is “1” andthe “address 2” field describes, as “TA” or “BSSID”, the MAC address ofthe self station or the address of a terminal in the BSS to which theself station belongs, or when the “From DS” field of the received frameis “0” and the “address 1” field describes, as “BSSID” or “DA”, the MACaddress of the self station or the address of a terminal in the BSS towhich the self station belongs, the flow advances to step S414, and thebase station AP makes an operation for suppressing transmission of adata frame from the self station (sets the NAV).

If it is determined in step S413 that the received frame is other thanthe aforementioned frames, i.e., it is a data frame, which is used forcommunicating in another BSS different from the BSS to which the selfstation belongs, the base station AP discards the frame withoutprocessing it (without setting any NAV) (step S415).

The data frame receiving process operation in the terminal STA will beexplained below.

Upon receiving a frame (step S401), basically, if the received frame isnot addressed to the base station (“To DS”=0) and a address of the selfapparatus is described as “DA” in the received frame (step S403), theflow advances to step S404, and the terminal STA executes a receivingprocess for the received frame.

In step S403, when the address field of the received frame does notdescribe the address of the self apparatus as “DA”, if the address ofthe base station in the BSS to which the self apparatus belongs isdescribed as “BSSID”, “SA”, “DA”, “TA”, or “RA” (step S405), the flowadvances to step S406, and the terminal STA executes an operation forsuppressing transmission of a data frame from the self apparatus (setsthe NAV).

If the received frame is addressed to the base station (step S402), andthe address field of the received frame contains the address of the basestation in the BSS to which the self apparatus belongs, as “BSSID”,“SA”, “DA”, “TA”, or “RA” (step S408), the flow advances to step S409,and the terminal STA executes a operation for suppressing transmissionof a data frame from the self apparatus (sets the NAV).

In step S408, if the address field of the received frame does notcontain any address of the base station in the BSS to which the selfapparatus belongs, the flow advances to step S410, and the terminal STAdiscards the frame without processing it (without setting any NAV).

More specifically, as shown in FIG. 11B, in step S402, if the “To DS”field of the received frame is “0”, and the received frame is notaddressed to the base station, the flow advances to step S403. In stepS403, if the self MAC address is described as “DA” in “address 1” of thereceived frame, the terminal STA executes a receiving processcorresponding to the received frame (step S404).

If the received frame is not addressed to the self apparatus (stepS403), the flow advances to step S405. In step S405, if the receivedframe is not addressed to the self apparatus but addressed to a terminalor base station in the BSS to which the self apparatus belongs, theterminal STA sets the NAV. That is, if the “From DS” field in thereceived frame is “1” and the “address 2” field describes the address ofthe base station of the BSS to which the self apparatus belongs, as“BSSID” or “TA”, or if the “From DS” field is “0” and the “address 3”field describes the address of the base station of the BSS to which theself apparatus belongs, as “SA”, the flow advances to step S406, and theterminal STA sets the NAV.

In step S405, if the received frame is addressed neither to the selfapparatus nor to a terminal or base station in the BSS to which the selfapparatus belongs, the terminal STA discards the received frame (stepS407).

If the “To DS” field of the received frame is “1” and the received frameis addressed to the base station (step S402), the flow advances to stepS408. In step S408 if the address of the base station in the BSS towhich the self apparatus belongs is described as the destination orsource of the received frame, i.e., the address of the base station inthe BSS to which the self apparatus belongs is described in “address 1”or “address 2” as “BSSID”, “RA”, “TA”, “SA”, or “DA”, the terminal STAsets the NAV (step S409).

In step S408, if the address of the base station in the BSS to which theself apparatus belongs is not described as the destination or source ofthe received frame, the flow advances to step S410, and the terminal STAdiscards the received frame.

In case of the base station AP, the aforementioned processes areexecuted by the receiving control unit 13, which controls thetransmitting control unit 14. In case of the terminal STA, theaforementioned processes are executed by the receiving unit 201, whichcontrols the transmitting unit 207.

In this way, upon receiving a frame, if the received frame is a dataframe which is used for communicating only in another BSS different fromthe BSS to which the self station belongs (although the NAV is set inthe conventional system), the base station AP discards the frame withoutprocessing it (without setting any NAV). Therefore, if there is a frameto be transmitted to another base station, the base station AP canquickly start transmission of frame to the base station in the otherbase station. In this manner, upon receiving a frame to be exchangedwith the other base station, the base station deliberately permits radiowave collision, and gives priority to communications between the otherbase station and the self station, thus improving the efficiency ofcommunications between the other base station and the self station.

Upon receiving a frame, if the address field of the received frame doesnot contain the address (as “BSSID” or the like) of the base station inthe BSS to which the self apparatus belongs (although the NAV is set inthe conventional system), the terminal STA discards the frame withoutprocessing it (without setting any NAV). Hence, if there is a frame tobe transmitted, the terminal STA can efficiently start transmissionwithout idle transmission wait time.

Third Embodiment

The third embodiment will explain communications between base stationswhen one of the base stations AP1 and AP2 (e.g., AP2 in this case) has adirectional antenna in the wireless LAN system shown in FIG. 1. That is,a case will be explained below wherein the base station AP2 directs abeam of the directional antenna to the base station AP1 forcommunication between the base stations. In the following description, acase will be exemplified wherein the base station AP2 has a directionalantenna, and the same applies to a case wherein the base station AP1 hasa directional antenna.

Note that the process for making the base station AP1 recognize the basestation AP2 as a base station uses the method described in the first orsecond embodiment.

(Overall Arrangement)

FIG. 12 shows a wireless communication system according to the thirdembodiment, and the same reference numerals denote the same parts as inFIG. 1. The base station AP2 comprises a directional antenna 2 in placeof the antenna 20 in FIG. 3. The directional antenna 2 forms onerelatively narrow directive pattern (to be referred to as a directivebeam or antenna beam hereinafter) 3-1 to communicate with one of thebase station AP1 and the terminals STA21 and STA22.

As shown in FIG. 12, the base station AP2 may be set at a specific fixedposition, and may be connected to the wired network 5.

(About Base Station Apparatus)

The arrangement of the base station AP1 according to this embodiment issubstantially the same as that in FIG. 3, except that the antenna 20 isreplaced by directional antenna 2.

An example of the detailed arrangement of the directional antenna 2 willbe explained below using FIG. 13.

As shown in FIG. 13, the directional antenna 2 has an antenna element30-1, transmission/reception switch 31-1, low-noise amplifier (LNA)32-1, down converter 33-1, receiving beam forming unit 35-1,transmitting beam forming unit 36-1, up converter 38-1, high-frequencypower amplifier (HPA) 39-1, and beam controller 40.

The operation of the directional antenna 2 will be described below. AnRF signal received by the antenna element 30-1 is input to the LNA 32-1via the transmission/reception switch 31-1, and is amplified to apredetermined level. The RF signal amplified by the LNA 32-1 is input tothe down converter 33-1 which converts the frequency band of the RFsignal from the radio frequency (RF) to the intermediate frequency (IF)or baseband (BB), and the converted signal is input to the receivingbeam forming unit 35-1.

The receiving beam forming unit 35-1 forms a receiving antenna beam byweighting and combining the input signal by a receiving complexweighting factor set by the beam controller 40. A signal correspondingto the receiving antenna beam from the receiving beam forming unit 35-1is supplied to the receiver 11 in FIG. 3.

On the other hand, the transmitting beam forming unit 36-1 receives atransmitting signal TS1 from the transmitter 12 in FIG. 3. Thetransmitting beam forming unit 36-11 multiples the input transmittingsignal by a transmitting complex weighting factor set by the beamcontroller 40.

The output signal from the transmitting beam forming unit 36-1 is inputto the up converter 38-1. The up converter 38-1 converts the frequencyband of that output signal (transmitting signal) from the intermediatefrequency (IF) or baseband (BB) to the radio frequency (RF), and inputsthe converted signal to the HPA 39-1. The transmitting signal amplifiedby the HPA 39-1 is supplied to the antenna element 30-1 via the switch31-1, and is then transmitted to the base station AP or terminal STA.

The beam controller 40 sets the receiving complex weighting factor forthe receiving beam forming unit 35-1, and the transmitting complexweighting factor for the transmitting beam forming unit 36-1. In thiscase, weighting factors used to communicate with an identical basestation or terminal are set.

In this embodiment, the base station AP2 uses relative positioninformation of the base station AP1 with reference to the position ofthe base station AP2 so as to direct a beam of the directional antennatoward the base station AP1.

In this case, as shown in FIG. 14, after an authentication process(authentication, association) with the base station AP1 (see thedescription of FIG. 5), the base station AP2 may request the basestation AP1 to send position information (x1, y1, z1) of the basestation AP1 (step S311). In this manner, the position information (x1,y1, z1) of the base station AP1 is obtained (step S312). The basestation AP2 calculates the difference between the position information(x1, y1, z1) of the base station AP1 and position information (x2, y2,z2) of the self station to obtain the relative position information ofthe base station AP1.

The base station AP2, which has acquired the relative positioninformation of the base station AP1, sets the receiving and transmittingcomplex weighting factors based on the acquired information, to directthe beam of the directional antenna toward the base station AP1, anduses these factors in wireless communications with the base station AP1later (step S313).

In this case, the base stations AP1 and AP2 may recognize their positioninformation using a GPS (Global Positioning System) or the like, orbased on value predetermined to each of the base station.

Or the base station AP2 may recognize the position information of thebase station AP1 based on, e.g., user's input. In such case, when theposition information of the base station AP1 is input as absoluteposition information (x1, y1, z1), the base station AP2 calculates thedifference from its absolute position information (x2, y2, z2) to obtainrelative position information of the base station AP1 with reference tothe position of the base station AP2. Alternatively, relative positioninformation may be given in advance.

The position information is used to set weighting factors for formingthe beam of the directional antenna. If the base stations are nearly atthe same levels, the weighting factors may be set by omittinginformation of the z-axis or the like.

As described above, according to the third embodiment, the communicationquality between the base stations can be improved using a directivebeam. Especially, when the third embodiment is used in combination withthe second embodiment, the arrangement of the third embodiment iseffective to reduce the probability of collision of radio signals, whichmay occur when NAV is not set.

Another method of determining the weighting factors of the directionalantenna in the base station AP2 will be explained below. That is, thebase station AP2 may indirectly obtain the position information of thebase station AP1 from frames exchanged between the base stations.

The frames to be exchanged include all frames to be exchanged betweenthe base stations such as frames used in authentication and association,combinations of RTS/CTS upon transmitting a data frame, a data frame andACK response, and the like.

The base station AP2 sets weighting factors of the directional antennaon the basis of the angle of arrival of a frame transmitted from thebase station AP1. The base station AP2 continuously receives framestransmitted from the base station AP1 and corrects the angle of a beamspread of the directional antenna if it determines that it is necessary.When it is determined that the angles of arrival falls within a givenrange after some frame exchanges, beam parameters may be set to narrowdown the beam width to that range.

The base station AP2 transmits a signal to the base station AP1 using anantenna beam formed based on the set weighting factors.

This method can be used to improve the accuracy of the angle of beamspread of the directional antenna even when, for example, the basestation AP2 has already acquired the position information of the basestation AP1 in step S312 in FIG. 14.

In this manner, since the base station AP2 corrects the weightingfactors of its directional antenna on the basis of the angle of arrivalof the received frame, the accuracy of the weighting factors used toform the bean of the directional antenna can be improved, and the beamwidth can be narrowed down. In this manner, the influences ofinterference from the base station AP2 on another base station orterminal STA using an identical channel can be further reduced, thusexpanding the communication capacity.

Especially, when this embodiment is combined with the second embodiment,collision of radio signals, which may occur when NAV is not set, can bereduced.

In the third embodiment, only the base station AP2 has a directionalantenna and exchanges frames by directing the antenna beam toward thebase station AP1 in communications between the base stations. However,the present invention is not limited to such specific cases, and boththe base stations may have directional antennas, and may exchange framesby directing antenna beams toward the partner base stations. In suchcase, the arrangement of the base station AP1 is the same as that shownin FIG. 13 described in the third embodiment.

Since the base station AP1 sets the weighting factors to direct the beamof its directional antenna toward the base station AP2, it must alsorecognize the position information of the base station AP2. In thiscase, the base station AP1 can execute the procedure in steps S311 toS313, as has been explained above with reference to FIG. 14.

Since the two base stations that are to undergo communications directthe beams of their directional antennas to each other so as to exchangeframes, the communication quality between the base stations can befurther improved compared to a case wherein only one of the two basestation has a directional antenna.

Therefore, when the base station AP2 alone has the directional antenna,only the influences of interference from the base station AP2 on anidentical channel can be reduced, however, by the base station AP1 alsousing a directional antenna, the influences of interference from thebase station AP1 on an identical channel can also be reduced, andcommunication capacity can be further expanded.

Especially, when this embodiment is combined with the second embodiment,collision of radio signals, which may occur when NAV is not set, can befurther reduced.

Upon determining the weighting factors of the directional antenna, thebase station AP1 may indirectly acquire the position information of thebase station AP2 from frames exchanged between the base stations, as inthe above description of the third embodiment.

The base station AP2 having the directional antenna according to thethird embodiment may communicate with another base station using thedirective beam directed toward the partner base station, and maycommunicate with terminals by canceling the directivity (i.e. by usingan omnidirectional beam).

For example, as shown in FIG. 14, the base station AP2 receives a beaconframe from the base station AP1, and sets weighting factors fordirecting the beam of the directional antenna toward the base stationAP1, via the authentication process with the base station AP1. As shownin FIG. 10, when the terminal STA21 in the second BSS transmits a dataframe which includes the MAC address of the terminal STA11 in the firstBSS as the DA (destination address), the base station AP2 communicateswith the terminal STA21 using an omnidirectional beam in steps S351 toS354 in FIG. 10, and communicates with the base station AP1 using thedirective beam in step S355 in FIG. 10.

When the base station AP1 transmits a frame addressed to the terminalSTA21 in the second BSS via the base station AP2, the base station AP2directs the beam of the directional antenna toward the base station AP1,and receives a predetermined number of data frames from the base stationAP1. After that, the base station AP2 cancels the directivity toward thebase station AP1 (by setting uniform weighting factors), and thentransmits that received frames to the terminal STA21 by usingomnidirectional beam.

Note that the final destination (DA) of frames to be transmitted fromthe base station AP1 may be a plurality of terminals including the basestation AP2.

When the base station AP2 determines that data frames to be receivedstill remain after it has received a predetermined number of data framestransmitted from the base station AP1, it directs the beam of thedirectional antenna toward the base station AP1 again, and receivesthose data frames.

The base station AP2 determines that data frames to be received of thoseto be transmitted from the base station AP1 still remain, for example,when transmission from the base station AP1 is detected when the basestation AP2 sets the antenna to be omnidirectional, or when the basestation AP2 receives a message indicating the presence of remainingframes in the last frame upon receiving a predetermined number of dataframes. Even when the base station AP2 cannot detect the presence of(remaining) data frames to be received, it may direct the beam of thedirectional antenna toward the base station AP1 again after an elapse ofa predetermined period of time, and can receive data frames transmittedby a resend process from the base station AP1.

The base station AP2 can communicate with the terminals STA21 and STA22in the second BSS by canceling the directionality of the antenna beamdirected toward the base station AP1 to set omnidirectionality.

Upon communicating with the base station AP1, the base station AP2 maycancel directionality of the directional antenna directed toward thebase station AP1 to set omnidirectionality during a time interval inwhich the base station AP1 transmits beacon frames.

The base station AP2 receives an RTS frame or the like as one of controlframes specified by IEEE802.11 (including IEEE802.11a and IEEE802.11b)from the base station AP1 while it sets the antenna 2 to beomnidirectional. When the base station AP2 determines that data framesare transmitted from the base station AP1, it directs the beam of theantenna 2 toward the base station AP1 to receive the frames, and returnsa response as needed.

With this method, the base station AP2 does not assign a beam of theantenna 2 to the base station AP2 to receive beacon frames from the basestation AP1 while data need not be exchanged with the base station AP1after authentication. Therefore, the beam can be assigned tocommunications with the terminals STA21 and STA22 in the second BSS towhich the base station AP2 belongs, and wireless resources can beefficiently used in communications.

Upon exchanging data frames, the communication quality of which must beimproved, with the base station AP1, the base station AP2 directs thebeam of the antenna 2 toward the base station AP1 again to meet a highcommunication quality requirement.

Fourth Embodiment

The fourth embodiment will explain a case wherein the base station AP2has an adaptive array antenna. That is, a case will be described whereinthe base station AP2 simultaneously communicates with the partner basestation AP1 and the terminals STA21 and STA22 in the second BSS in asingle channel using beams of a plurality of antennas. Communicationsbetween the base station AP2, and the base station AP1 and terminalsSTA21 and STA22 are made based on SDMA (Space Division Multiple Access).Note that this embodiment may use the method described in the first orsecond embodiment as the process for making the base station AP1recognize the base station AP2 as a base station.

(Overall Arrangement)

FIG. 15 shows a wireless communication system according to the fourthembodiment, and the same reference numerals denote the same parts asthose in FIGS. 1 and 12. The base station AP2 comprises an adaptivearray antenna 25. The adaptive array antenna 25 forms a plurality ofrelatively narrow directive patterns (to be referred to as directivebeams or antenna beams hereinafter) 3-1 to 3-3. As shown in FIG. 15, thebase station AP2 may be set at a specific fixed position, and may beconnected to the wired network 5.

With such antenna beams 3-1 to 3-3, the base station AP2 cansimultaneously communicate with a plurality of terminals (for example,terminals STA21 and STA22 in this case) and another base station AP1 ina single channel. That is, communications between the base station AP2,and the terminals STA21 and STA22 and base station AP1 are made based onSDMA. Note that this embodiment will exemplify a case wherein the basestation AP2 forms three antenna beams 3-1 to 3-3, and simultaneouslycommunicates with the two terminals STA21 and STA22 and the base stationAP1, but the number of antenna beams, and the number of terminals whichare to undergo simultaneous communications may be an arbitrary valueequal to or larger than 2. The terminals STA21 and STA22 are normallyset at fixed positions, but may be movable bodies or may be mounted onmovable bodies.

(About Base Station Apparatus)

The arrangement of the base station AP2 according to this embodimentwill be explained below using FIG. 16.

Receivers 11-1 to 11-3 respectively receive signals transmitted fromother terminals (for example, the terminals STA21 and STA22), and basestation AP1 via antenna beams 3-1 to 3-3 of the adaptive array antenna25. The receivers 11-1 to 11-3 execute processes including demodulationand decoding for the received signals to generate received signals RS1to RS3.

On the other hand, transmitters 12-1 to 12-3, respectively generatetransmitting signals TS1 to TS3 to be transmitted to the terminals STA21and STA22, and base station AP1, and supplies these transmitting signalsTS1 to TS3 to the adaptive array antenna 25. The transmitting signalsTS1 to TS3 are respectively transmitted to the terminals STA21 andSTA22, and base station AP1 via the antenna beams 3-1 to 3-3 of theadaptive array antenna 25.

The received signals RS1 to RS3 output from the receivers 11-1 to 11-3are input to a receiving control unit 13 and undergo predeterminedreceiving processes.

A transmitting control unit 14 executes a transmitting process includinggeneration of a packet or a frame to be broadcasted or unicasted to theterminals STA21 and STA22, and base station AP1. The packet or framegenerated by the transmitting control unit 14 are transmitted to theterminals STA21 and STA22, and base station AP1 as transmitting signalsTS1 to TS3 via the transmitters 12-1 to 12-3.

(About Adaptive Array Antenna)

An example of the detailed arrangement of the adaptive array antenna 25will be described below using FIG. 17.

As shown in FIG. 17, the adaptive array antennas 25 comprises antennaelements 30-1 to 30-3, transmission/reception switches 31-1 to 31-3,low-noise amplifiers (LNAs) 32-1 to 32-3, down converters 33-1 to 33-3,distributors 34-1 to 34-3, receiving beam forming units 35-1 to 35-3,transmitting beam forming units 36-1 to 36-3, combiners 37-1 to 37-3, upconverters 38-1 to 38-3, high-frequency power amplifier (HPAs) 39-1 to39-3, and beam controller 40.

The transmission/reception switches 31-1 to 31-3, LNAs 32-1 to 32-3,down converters 33-1 to 33-3 distributors 34-1 to 34-3, combiners 37-1to 37-3, up converters 38-1 to 38-3, and HPAs 39-1 to 39-3 are arrangedas many as the antenna elements 30-1 to 30-3 (three elements in thisexample) in correspondence with the antenna elements 30-1 to 30-3. Onthe other hand, receiving beam forming units 35-1 to 35-3 andtransmitting beam forming units 36-1 to 36-3 are arranged as many as theantenna to be formed by the adaptive array antenna 35 (three beams inthis example). The number of antenna beams can be either smaller orlarger than the number of antenna elements 30-1 to 30-3.

The operation of the adaptive array antenna 25 will be described below.RF signals received by the antenna elements 30-1 to 30-3 arerespectively input to the LNA5 32-1 to 32-3 via thetransmission/reception switches 31-1 to 31-3, and are amplified to apredetermined level. The RF signals amplified by the LNA5 32-1 to 32-3are respectively input to the down converters 33-1 to 33-3, each ofwhich converts the frequency band of the RF signal from the radiofrequency (RF) into the intermediate frequency (IF) or baseband (BB),and are then input to the distributors 34-1 to 34-3.

The distributor 34-1 distributes the output signal from the downconverter 33-1 to the receiving beam forming units 35-1 to 35-3. Thedistributor 34-2 distributes the output signal from the down converter33-2 to the receiving beam forming units 35-1 to 35-3. The distributor34-3 distributes the output signal from the down converter 33-3 to thereceiving beam forming units 35-1 to 35-3.

The receiving beam forming units 35-1 to 35-3 weight and combine theinput signals in accordance with receiving complex weighting factors setby the beam controller 40, thus forming a plurality of receiving antennabeams. Signals corresponding to the receiving antenna beams from thereceiving beam forming units 35-1 to 35-3 are respectively supplied tothe receivers 11-1 to 11-3 in FIG. 16.

On the other hand, the transmitting beam forming units 36-1 to 36-3respectively receive transmitting signals TS1 to TS3 from thetransmitters 12-1 to 12-3 in FIG. 16. The transmitting beam formingunits 36-1 to 36-3 respectively multiply the input transmitting signalsby a plurality of transmitting complex weighting factors set by the beamcontroller 40.

A plurality of output signals from the transmitting beam forming unit36-1 are input to the combiners 37-1 to 37-3, and those from thetransmitting beam forming units 36-1 and 36-2 are also input to thecombiners 37-1 to 37-3. Each of the combiners 37-1 to 37-3 combines theplurality of input signals into one signal.

The output signals from the combiners 37-1 to 37-3 are respectivelyinput to the up converters 38-1 to 38-3, each of which converts thefrequency band of the signal from the intermediate frequency (IF) orbaseband (BB) into the radio frequency (RF), and the converted signalsare output to the HPAs 39-1 to 39-3. The transmitting signals amplifiedby the HPAs 39-1 to 39-3 are respectively supplied to the antennaelements 30-1 to 30-3 via the switches 31-1 to 31-3, and are transmittedto the terminals and base station.

The beam controller 40 sets receiving complex weighting factors in thereceiving beam forming units 35-1 to 35-3, and sets transmitting complexweighting factors in the transmitting beam forming units 36-1 to 36-3.In such case, the beam controller 40 sets weighting factors used tocommunicate with an identical terminal in corresponding transmitting andreceiving beam forming units (e.g., the receiving beam forming unit 35-1and transmitting beam forming unit 36-3).

In the following description, a case will be exemplified wherein thebase station AP2 has an adaptive array antenna. Also, the same appliesto a case wherein the base station AP1 has an adaptive array antenna. Orboth the base stations AP1 and AP2 may have adaptive array antennas.

The base station AP2 according to the fourth embodiment forms directivebeams, which are respectively assigned to another base station (e.g.,the base station AP1), and the terminals STA21 and STA22, using theadaptive array antenna 25, and communicates with them. As a result, onthe terminal side, the opportunity of receiving signals directed fromthe base station AP2 to terminals other than the self terminal isreduced. Hence, interference can be reduced, and the number of terminalswhich can establish wireless connection to the base station AP2, i.e.,the communication capacity in the BSS of the base station AP2, can beincreased.

Note that a directive beam may be assigned to each group of a pluralityof terminals. In such case, the arrangement and control of the adaptivearray antenna in the base station AP2 can be facilitated while obtainingnearly the same effect as that obtained upon assigning beams to allterminals.

Upon communicating wirelessly with the base station AP1, the basestation AP2 may check the presence/absence of directive beam control ofthe base station AP1 on the basis of the transmitting power upontransmitting frame from the base station AP1, the received powermeasured upon receiving frame transmitted from the base station AP1, andthe type of received frame, and may adjust transmitting power upontransmitting frame to the base station AP1 on the basis of the checkingresult.

Or upon communicating wirelessly with the base station AP1, the basestation AP2 may check the presence/absence of directive beam control ofthe base station AP1 on the basis of the received power measured uponreceiving frame transmitted from the base station AP1, and the type ofreceived frame, and may adjust transmitting power upon transmittingframe to the base station AP1 on the basis of the checked result.

In a wireless LAN system that uses CSMA and is based on IEEE802.11(including IEEE802.11a and IEEE802.11b), a terminal makes carrier sensebefore frame transmission to a base station to which the terminal is totransmit the frame (data). Carrier sense includes a Physical CarrierSense Mechanism for checking based on the received signal level if awireless communication medium is busy or idle, and a Virtual CarrierSense Mechanism for estimating based on reservation information includedin a received signal.

If it is determined based on this carrier sense that the received levelof a signal from another terminal to still another terminal including abase station is larger than a given threshold value, or if a frameincluding channel reservation information is received from anotherterminal, the terminal postpones frame transmission. If a wirelesscommunication medium becomes idle after an elapse of a randomtransmission wait time, the terminal starts connection with a basestation or terminal, or transmits a frame in which the address of a basestation or another terminal is designated as the destination whenconnection has already been established.

On the other hand, according to SDMA, when an adaptive array antennaequipped in a base station apparatus forms a plurality of antenna beamsthat can reduce mutual interference, the communication quality can beimproved, and simultaneously communications between the base stationapparatus and a plurality of terminal apparatuses can be implemented. Awireless LAN system based on CSM1 can also enjoy such merits by applyingSDMA.

However, when SOMA is simply applied to the wireless LAN system based onCSMA, the following problem is posed.

In general, it is assumed that a terminal does not have any directionalantenna such as an adaptive array antenna, because the arrangement andcontrol of which are complex. Hence, when frame transmission is madebetween base stations, another terminal determines by the carrier sensefunction that the wireless communication medium is busy, and waits frame(packet) transmission. For this reason, even when the base stationcomprises an adaptive array antenna, communications that exploit SDMA inwhich another base station and a plurality of terminals simultaneouslycommunicate with each other using a single channel cannot be efficientlymade in a wireless communication system that adopts CSMA.

To solve this problem, when at least one of transmitting power controland carrier sense level control is done in wireless communicationsbetween base stations, the number of multiple accesses can be increasedand, hence, the transmission efficiency upon adopting SDMA can beimproved.

FIG. 18 shows an example of the arrangement of principal part of thebase station AP2, which implements a function of adjusting transmittingpower upon transmitting frame from the base station AP2 toward the basestation AP1. Of course, the base station AP1 may execute transmittingpower control as in the base station AP2 using the arrangement shown inFIG. 18. The following explanation will be given while taking the basestation AP2 as an example, but the same applies to the base station AP1.

A case will be explained below wherein the base station AP1 has anadaptive array antenna, and the base station AP2 has a function ofadjusting transmitting power. However, the present invention is notlimited to such specific example, and the base station AP2 may have anadaptive array antenna, and the base station AP1 may have a function ofadjusting transmitting power. Or both the base stations AP1 and AP2 mayhave adaptive array antennas, and the function of adjusting transmittingpower.

The base station AP which has the adaptive array antenna transmitsbeacon frames by transmitting power that a plurality of terminals STAsaround that base station AP can receive, at given time intervals. Thebeacon frames are transmitted using an omnidirective pattern since theymust be transmitted to another base station AP and all terminals STAsand, hence, are broadcasted. On the other hand, since frames inauthentication and association processes must be individually exchangedwith another base station AP or each terminal STA, i.e., must beunicasted, a directive beam is used.

Hence, focusing attention on this feature, upon receiving frame from thebase station AP1, the base station AP2 checks the type of received framefirst. That is, it is identified if the received frame is a frametransmitted using an omnidirective pattern (or a omnidirective beam)(for example, a beacon frame specified by IEEE802.11 (includingIEEE802.11a and IEEE802.11b)) or a frame transmitted by forming adirective beam if the base station AP1 can form it (for example, anauthentication frame, association frame, or the like specified byIEEE802.11 (including IEEE802.11a and IEEE802.11b)). Then, the basestation AP2 estimates the gain of a directive beam upon unicasting aframe addressed to the base station AP2 from the base station AP1 usingtransmitting power information of frame such as a beacon frame, which istransmitted using an omnidirective beam, transmitting power informationof frame such as an authentication or association frame, which istransmitted by forming a directive beam if the base station AP1 can formit, and received power upon receiving such two types of frames inpractice.

It is then determined based on that estimation result if the basestation AP1 forms a directive beam to the base station AP2 (thepresence/absence of directive beam control), in other words, the basestation AP1 is making SDM (Space Division Multiple Access) with respectto the base station AP2. If it is determined that the base station AP1is making SDMA, the base station AP2 adjusts transmitting power of frameaddressed to the base station AP1.

As shown in FIG. 18, the base station AP2 comprises a received powermeasuring unit 102, received frame type detection unit 103, transmittedpower detection unit 104, beam gain estimating unit 105, and transmitterpower control unit 106, in addition to the arrangement shown in FIGS. 3and 16.

The received power measuring unit 102 measures electric power (receivedpower) induced at the antenna 20 upon receiving frame data by thereceiving control unit 13. Note that the directional antenna or adaptivearray antenna 25 may replace the antenna 20.

The received frame type detection unit 103 determines based oninformation such as “type”, “subtype”, and the like in a MAC frameobtained by the receiving control unit 13 if that MAC frame isbroadcasted or unicasted.

That is, the unit 103 determines based on “type” and “subtype” in theMAC frame if that MAC frame is a beacon frame (broadcasted frame) orauthentication or association frame (unicasted frame).

Note that the received frame type detection unit 103 can also determinebased on the destination address “IDA” in a MAC frame obtained by thereceiving control unit 13 if that MAC frame is broadcasted or unicasted.However, in this embodiment, the former case will be exemplified.

The transmitted power detection unit 104 extracts, from a MAC frameobtained by the receiving control unit 13, information (transmittingpower information) associated with transmitting power upon transmittingthat MAC frame from the base station AP1. The transmitting powerinformation may be a power value itself, but may be a relative value(e.g., a level value) with reference to a predetermined value. That is,the base station AP2 can determine a variation of transmitting power onthe basis of this information. Assume that the transmitting powerinformation is stored at a predetermined position in the MAC frame. Forexample, this information is preferably presented using an undefined(reserved) field in “frame body” in the IEEE802.11 (includingIEEE802.11a and IEEE802.11b) standard. However, the present invention isnot limited to such a specific example, and the transmitting powerinformation may be presented using an undefined field which is not usedin the MAC frame upon operation of the wireless communication system.

For example, the transmitting power information may be expressed usingone or a plurality of undefined status codes in a status code field in“frame body” in case of an authentication frame.

In this example, the base station AP2 estimates the gain of a directivebeam upon unicasting a frame addressed to the base station AP2 from thebase station AP1 using transmitting power information of frame which istransmitted by forming a directive beam if the base station AP1 can formit, and received power upon receiving such frame in practice. However,the present invention is not limited to such specific example. Forexample, the base station AP2 estimates the gain of a directive beamupon unicasting a frame addressed to the base station AP2 from the basestation AP1 using received power upon receiving such frame without usingany transmitting power information of frame which is transmitted byforming a directive beam if the base station AP1 can form it. However,when the transmitting power information is used as in the former case,the reliability of the estimated (calculated) gain can be improved. Whenno transmitting power information is used as in the latter case, thetransmitted power detection unit 104 in FIG. 18 may be omitted.

Alternatively, transmitting power values of various MAC frames may bedetermined in advance, and may be pre-stored in the transmitted powerdetection unit 104 in correspondence with the types of MAC frames suchas beacon, authentication, association, and the like. In such case, whenthe received frame type detection unit 103 detects the type of receivedMAC frame, the transmitted power detection unit 104 reads outtransmitting power corresponding to that type.

The beam gain estimating unit 105 estimates the gain (directive gain) ofa directive beam of data received by the receiving control unit 13 onthe basis of the type of a received frame detected by the received frametype detection unit 103 (a broadcasted frame (e.g., a beacon frame) or aunicasted frame (e.g., an authentication or association frame)), thereceived power measured by the received power measuring unit 102, andthe transmitting power information of that received frame obtained bythe transmitted power detection unit 104. Based on the estimateddirective gain, the presence/absence of directive beam control of thebase station AP1 is determined, and if the directive gain value (level)is equal to or higher than a predetermined level, it is determined thatthe base station AP1 is implementing SDMA.

When the beam gain estimating unit 105 determines that the base stationAP1 is implementing SDM1, the transmitter power control unit 106 lowerstransmitter power of frame addressed to the base station AP1 by, e.g., apredetermined level. The transmitting power of frame addressed to thebase station AP1 is preferably the smallest possible transmitting powerwithin the receivable range at the base station AP1, i.e., the minimumrequired transmitting power. Note that the circuit itself forimplementing transmitter power control is known to those who are skilledin the art.

FIG. 19 is a flow chart for explaining the processing operation of thebase station AP2.

Referring to FIG. 19, if the power supply is turned on (step Si), thebase station AP2 is set in a receiving mode, and is ready forcommunications by establishing connection in response to a request from,e.g., the base station AP1 or terminal STA (step S2).

Assume that a data transmission request is generated at the base stationAP2 (by, e.g., user's operation) in the receiving mode, and a connectionrequest for connecting the self station to the base station AP1 isgenerated (step 53). In such cases, authentication and associationprocesses are executed between the base stations AP2 and AP1 (steps S4and S5).

Note that authentication and association comply with IEEE802.11(including IEEE802.11a and IEEE802.11b).

If authentication and association have succeeded and connection betweenthe base stations AP2 and AP1 is established, the base station AP2 cancommunicate with the base station AP1 via this connection. That is, thebase station AP2 is set in a communication mode (step S6).

Note that authentication and association need only be done once betweenapparatuses which must establish wireless connection (need not be doneevery time a data frame is transmitted).

Upon breaking wireless connection with the base station AP1, the basestation breaks the established connection via disassociation anddeauthentication processes (steps S8 and S9), and goes to the receivingmode again (step S2).

In FIG. 19, the processes executed upon establishing/breaking connectionbetween the base stations AP1 and AP2 have been exemplified. The sameapplies to processes executed upon establishing breaking connectionbetween the terminal STA and the base station AP2.

Note that disassociation and deauthentication comply with IEEE802.11(including IEEE802.11a and IEEE802.11b).

The transmitting power control procedure upon transmitting frames fromthe base station AP2 to the base station AP1 will be explained belowwith reference to FIG. 20.

The base station AP1 periodically transmits beacon frames (step S101).In principle, the base station AP2 can receive beacon frames not only inthe receiving mode in step S2 in FIG. 19, i.e., but duringauthentication and association processes in steps S4 and S5, anddisassociation and deauthentication processes in steps S8 and S9.

For example, in the base station AP2, if the received frame typedetection unit 103 determines in the receiving mode that a framereceived via the antenna 20, directional antenna 2, or adaptive arrayantenna 25 is a beacon frame, the beam gain estimating unit 105 receivesat least received power of the beacon frame measured by the receivedpower measuring unit 102. Note that the beam gain estimating unit 105may receive transmitting power information from the beacon frame or fromthat stored in advance in correspondence with the beacon frame from thetransmitted power detection unit 104 (step S102), so as to estimate thegain more accurately, as described above. Assume that the beam gainestimating unit receives the received power and transmitting powerinformation.

Every time a beacon frame is received, the received power measured atthat time and transmitting power information may be storedtime-serially.

After that, assume that a transmission request is generated at the basestation AP2 (step S3 in FIG. 19), and the control enters theauthentication process in step S4 in FIG. 19. In this case, thetransmitting control unit 14 of the base station AP2 transmits anauthentication frame with ATSN=1 as a frame that starts anauthentication request (and is addressed to the base station AP1) to thebase station AP1 (step S103). In this case, if transmitting power, whichwas set by the transmitter power control unit 106 previously upontransmitting frame to the base station AP1, is available, theauthentication frame with ATSN=1 is transmitted using that transmittingpower. Otherwise, that frame may be transmitted with defaulttransmitting power.

Note that ATSN is stored in “frame body” of the authentication frame.

Upon receiving the authentication frame with ATSN=1, the base stationAP1 sets a directive beam to be directed to the base station AP2 on thebasis of received power at that time and the like (step S104) That is,the base station AP1 sets the aforementioned weighting factorscorresponding to a direction in which the base station AP2 is present.

The base station AP1 transmits an authentication frame with ATSN=2(response to the authentication frame with ATSN=1) to the base stationAP2 using the set directive beam (step S105).

The authentication frame with ATSN=2 may contain transmitting powerinformation, as described above.

If the received frame type detection unit 103 determines that a framereceived via the antenna is an authentication frame with ATSN=2, thebeam gain estimating unit 105 receives at least the received power ofthat frame measured by the received power measuring unit 102.Furthermore, the beam gain estimating unit 105 may receive transmittingpower information, which is extracted from that frame or is pre-storedin correspondence with the authentication frame with ATSN=2, from thetransmitted power detection unit 104 (step S106). Assume that the beamgain estimating unit 105 receives the received power and transmittingpower information.

At this time, the beam gain estimating unit 105 and transmitter powercontrol unit 106 execute processes shown in FIG. 21 using the receivedpower and transmitting power information of the received beacon frameobtained in step S102 in FIG. 20, and those of the authentication framewith ATSN 2 obtained in step S105, so as to adjust the transmittingpower (step S107).

Referring to FIG. 21, the beam gain estimating unit 105 checks thepresence/absence of directive beam control of the base station AP1 onthe basis of the received power and transmitting power information ofthe received beacon frame obtained in step S102 in FIG. 20, and those ofthe authentication frame with ATSN 2 obtained in step S105 (step S201).That is, the presence/absence of directive beam control means whether ornot the base station AP1 focuses directionality toward the base stationAP2, i.e., whether or not an antenna beam is directed toward the basestation AP2.

For example, assume that the transmitting power information of thebeacon frame transmitted as an omnidirective pattern is “3”, and itsreceived power is “2”. Also, assume that the transmitting powerinformation of the authentication frame, which is assumed to have beentransmitted using a directive beam, is “3”, and its received power is“4”. Note that these numerical values are not actual power values butlevels corresponding to them. In this way, since the received powerincreases although the transmitting power of the base station AP1remains “3”, it is estimated that the base station AP1 executesdirective beam control with a gain of, e.g., level 1.

Likewise, assume that the transmitting power information of the beaconframe is “3”, and its received power is “2”. Also, assume that thetransmitting power information of the authentication frame is “4” andits received power is “4”. In this manner, when the degree of change intransmitting power does not correspond to that in received power, e.g.,when the transmitting power of the base station AP1 increases by “1” butthe received power increases by “2”, it is also estimated that the basestation AP1 executes directive beam control with a gain of, e.g., level1.

On the other hand, assume that transmitting power information of thebeacon frame is “3”, and its received power is “2”. Also, assume thatthe transmitting power information of the authentication frame is “4”and its received power is “3”. At this time, the received powerincreases by “1” in correspondence with the increment of “1” of thetransmitting power of the base station AP1, i.e., the degree of changein transmitting power corresponds to that in received power. In suchcase, since the base station AP1 executes transmitter power control andthe received power changes accordingly, it can be estimated that thebase station AP1 does not execute directive beam control using adirectional antenna.

Note that the presence/absence of directive beam control may beestimated on the basis of the reception results of two or more framessuch as beacon frames transmitted using omnidirective pattern, and twoor more frames such as authentication frames transmitted using directivepattern, thus further improving the estimation accuracy.

The base station AP2 checks the presence/absence of directive beamcontrol of the base station AP1 on the basis of the received power andtransmitting power information of the received beacon frame obtained instep S102, and those of the authentication frame with ATSN=2 obtained instep S105. Alternatively, the base station AP2 may execute such checkingprocess using only the received power, as described above. However,using both the received power and transmitting power information allowsmore accurate estimation of the presence/absence of directive beamcontrol of the base station AP1.

A case will be explained below wherein the beam gain estimating unit 105of the base station AP2 checks the presence/absence of directive beamcontrol of the base station AP1 without using any transmitting powerinformation of the received beacon frame and authentication frame.

In such case, the base station AP1 transmits frames such as beaconframes, authentication frames, and the like using predeterminedtransmitting power (e.g., “3”). For example, assume that the receivedpower of the received beacon frame obtained in step S102 in FIG. 20 is“2”, and that of the authentication frame with ATSN=2 obtained in stepS105 is “4”. In such case, although the base station AP1 transmits theseframes using identical transmitting power, the received power of a frameto be unicasted (authentication frame) is larger than that of a frame tobe broadcasted. In such case, it is estimated that the base station AP1executes directive beam control with a gain of, e.g., level 1.

If the base station AP2 determines in step S201 that the base stationAP1 executes directive beam control, the flow advances to step S202. Thebase station AP2 checks in step S202 if an antenna beam hasdirectionality that has been sufficiently focused toward the basestation AP2 by the base station AP1, and is strong enough to implementSDMA. That is, if the level of the estimated gain of the directive beamis equal to or higher than, e.g., a predetermined level (step S202), thebeam gain estimating unit 105 determines that it is possible toimplement SDMA.

For example, if the directive beam has a gain of level 1 or more, it isdetermined that the degree of focus of directionality in the basestation AP1 is enough to allow the base station AP2 to execute SDv1A (itis possible to implement SDMA).

However, step S202 is not always required, and may be omitted. In suchcase, if it is determined in step S201 that the base station AP1executes directive beam control, the flow jumps to step S204 whileskipping steps S202 and S203.

If the beam gain estimating unit 105 determines in step S203 that thebase station AP2 can execute SDMA, as described above, the flow advancesto step S204. In step S204, the transmitter power control unit 106 ofthe base station AP2 decreases the transmitting power of frame addressedto the base station AP1 by a predetermined level (it preferably setsminimum required transmitting power of frame addressed to the basestation AP1). That is, the transmitting power of frame addressed to thebase station AP1 is set to be a sufficiently small value within thereceivable range of the base station AP1.

Referring back to FIG. 20, if the transmitter power control has beendone according to FIG. 21 to set new transmitting power in step SI 07,the set transmitting power is used as that upon transmitting subsequentframe addressed to the base station AP1.

If authentication has succeeded, association is then executed accordingto the specifications of IEEE802.11. That is, if the transmitting poweris set in step S107, the transmitting control unit 14 of the basestation AP2 transmits an association request frame used to request startof association to the base station AP1 using the set transmitting power(step S108).

Upon normally receiving the association request frame, the base stationAP1 transmits an association response frame to the base station AP2 asits response (step S109). If association has succeeded, an accesscontrol phase comes to an end, and data frames are exchanged with thebase station AP1 (step S110) (corresponding to step S6 in FIG. 19)

A case will be explained below with reference to FIG. 22 wherein sharedkey authentication is made. Note that the same reference numerals denotethe same steps as in FIG. 20, and only differences will be explained. Incase of shared key authentication, after an authentication frame withATSN=2 is received in step S105, the base station AP2 transmits anauthentication frame with ATSN 3 to the base station AP1 (step S151). Insuch case, if transmitting power, which was set by the transmitter powercontrol unit 106 previously upon transmitting frame to the base stationAP1, is available, the authentication frame with ATSN 3 is transmittedusing that transmitting power. If no such transmitting power previouslyset by the transmitter power control unit 106 is available, that framemay be transmitted with default transmitting power.

Upon receiving the authentication frame with ATSN 3, the base stationAP1 re-sets a directive beam toward the base station AP2 on the basis ofthe received power at that time and the like (step S152). That is, thebase station AP1 re-sets the weighting factors corresponding to adirection in which the base station AP2 is present.

The base station AP1 transmits an authentication frame with ATSN 4 tothe base station AP2 using the set directive beam (step S153).

Note that the authentication frame with ATSN=4 may contain transmittingpower information, as described above.

If the received frame type detection unit 103 determines that framereceived via the antenna 20, directional antenna 2, or adaptive arrayantenna 25 is an authentication frame with ATSN=4, the beam gainestimating unit 105 receives the received power of that frame measuredby the received power measuring unit 102, and transmitting powerinformation, which is extracted from that frame or is pre-stored incorrespondence with the authentication frame with ATSN=4, from thetransmitted power detection unit 104 (step S154).

At this time, the beam gain estimating unit 105 and transmitter powercontrol unit 106 execute the processes shown in FIG. 21 using thereceived power and transmitting power information of the received beaconframe obtained in step S102 in FIG. 20, and those of the authenticationframe with ATSN=4 obtained in step S154, so as to set transmitting power(step S155)

After step S105, the same processes as in steps S106 and S107 in FIG. 20are executed, and using electric power set in the processes,authentication frame with ATSN=4 is transmitted in step S153 in FIG. 22,and is received. Then, transmitting power may be re-set in steps S154and S155.

The subsequent processing operations are the same as those in step S108and subsequent steps in FIG. 20.

In FIG. 22, the base station AP2 checks the presence/absence ofdirective beam control of the base station AP1 on the basis of thereceived power and transmitting power information of the received beaconframe, and those of the authentication frame with ATSN=4 so as to settransmitting power in step S155. Alternatively, the base station AP2 mayexecute such checking process using only the received power values ofthe received beacon frame and authentication frame with ATSN=4, asdescribed above. However, using both the received power and transmittingpower information allows more accurate estimation of thepresence/absence of directive beam control of the base station AP1.

A case will be explained below with reference to FIG. 23 wherein thebase station AP2 executes transmitter power control not inauthentication but in association. Note that the same reference numeralsdenote the same steps as in FIG. 20, and only differences will beexplained. That is, after the authentication frame with ATSN=2 isreceived in step S105, the flow jumps to step S108 while skipping stepsS106 and S107, and the base station AP2 transmits an association requestframe used to request start of association to the base station AP1 (stepS108). Upon normally receiving the association request frame, the basestation AP1 transmits an association response frame to the base stationAP2 as its response (step S109).

The association response frame may contain transmitting powerinformation, as described above.

In the base station AP2, if the received frame type detection unit 103determines that data received via the antenna 20, directional antenna 2,or adaptive array antenna 25 is an association response frame, the beamgain estimating unit 105 receives the received power of that framemeasured by the received power measuring unit 102, and transmittingpower information, which is extracted from that frame or is pre-storedin correspondence with the association response frame, from thetransmitted power detection unit 104 (step S161).

At this time, the beam gain estimating unit 105 and transmitter powercontrol unit 106 execute the processes shown in FIG. 21 using thereceived power and transmitting power information of the received beaconframe obtained in step S102, and those of the association response frameobtained in step S161, so as to set transmitting power (step S162).

If association has succeeded, the access control phase comes to an end,and data frames are exchanged with the base station AP1 (step S163)(corresponding to step S6 in FIG. 19).

In FIG. 23, the base station AP2 checks the presence/absence ofdirective beam control of the base station AP1 on the basis of thereceived power and transmitting power information of the received beaconframe, and those of the association response frame so as to settransmitting power in step S162. Alternatively, the base station AP2 mayexecute such checking process using only the received power values ofthe received beacon frame and association response frame, as describedabove. However, using both the received power and transmitting powerinformation allows more accurate estimation of the presence/absence ofdirective beam control of the base station AP1.

When the transmitting power is set in the procedure shown in FIG. 23,the setup processes of transmitting power using an authentication frameshown in steps S106 and 3107 in FIG. 20 and steps S154 and S155 in FIG.22 may be combined. In such a case, the transmitting power can be setmore accurately.

As described above, according to the fourth embodiment, the base stationAP2 checks if the base station AP1 executes directive beam control, onthe basis of the received power upon receiving a frame broadcasted fromthe base station AP1 and that upon receiving a frame unicasted from thebase station AP1. If it is determined that the directive beam control isexecuted, the base station AP2 may further check if the degree of focusof directionality is enough to implement SDMA. If it is determined thatthe base station AP1 executes directive beam control (with the degree offocus of directionality which is enough to implement SDMA), the basestation AP2 re-sets minimum required transmitting power used upontransmitting subsequent frame to the base station AP1. Since the basestation AP2 controls transmitting power upon transmitting frames to thebase station AP1, transmission of frame (unicasted) from the basestation AP2 to the base station AP1 can be prevented from interferingwith communications of nearby terminals STAs.

Also, according to the fourth embodiment, the base station AP2 checks ifthe base station AP1 executes directive beam control, on the basis ofthe received power upon receiving frame broadcasted from the basestation AP1 and transmitting power information corresponding to thatreceived frame, and received power upon receiving frame unicasted fromthe base station AP1 and transmitting power information corresponding tothat received frame. If it is determined that the directive beam controlis executed, the base station AP2 may further check if the degree offocus of directionality is enough to implement SDMA. If it is determinedthat the base station AP1 executes directive beam control (with thedegree of focus of directionality which is enough to implement SDMA),the base station AP2 re-sets minimum required transmitting power usedupon transmitting subsequent frame to the base station AP1. Since thebase station AP2 controls transmitting power upon transmitting frames tothe base station AP1, transmission of frame (unicasted) from the basestation AP2 to the base station AP1 can be prevented from interferingwith communications of nearby terminals STAs.

Upon comparing cases with and without transmitter power control by thebase station AP2, the former case assures sufficiently small receivedpower of a transmitting signal from the base station AP2 to the basestation AP1. For this reason, in the former case, the terminals STA21and STA22 in the BSS to which the base station AP2 belongs detect lessfrequently upon carrier sense that a wireless medium is busy. That is,when each of the terminals STA21 and STA22 does not detect any receivedpower of a signal transmitted from the base station AP2 to the basestation AP1, it never sets the NAV specified by IEEE802.11 (if the NAVis set, the terminal waits access to the base station AP2 for a periodof time designated by the NAV.

Therefore, the base station AP2 can implement SDMA with a plurality ofterminals STAs, and the number of multiple accesses can be increasedcompared to a case wherein the base station AP2 does not execute thetransmitter power control.

In the fourth embodiment, the base station AP2 checks if the basestation AP1 executes directive beam control. However, the presentinvention is not limited to such specific case, and the base station mayexecute the same processes for the terminals (terminals STA21 andSTA22).

The received frame type detection unit 103 of the fourth embodiment isused to identify if received frame is a frame which is assumed to bebroadcasted using an omnidirective pattern if the base station AP1 (orterminal STA21 or STA22) executes directive beam control, or a framewhich is assumed to be unicasted by forming a directive beam if the basestation AP1 executes directive beam control. In this case, the receivedframe type detection unit 103 extracts information such as “type”,“subtype”, and the like in a MAC frame obtained by the receiving controlunit 13, and identifies the type of received frame based on suchinformation, i.e., if the received frame is a beacon frame to bebroadcasted or an authentication! association frame to be unicasted.

In order to determine if the base station AP1 executes directive beamcontrol, broadcasted or unicasted frame can be identified by checkingthe destination address in frame transmitted from the base station AP1in addition to the aforementioned method. The received frame typedetection unit 103 checks the destination address (DA) of the receivedframe (MAC frame shown in FIG. 6). If the destination address is abroadcast address, the unit 103 determines that the received frame is abroadcasted frame; if the destination address is an address of the selfapparatus, the unit 103 determines that the received frame is aunicasted frame. In this way, whether the received frame is abroadcasted or unicasted frame can be identified.

Fifth Embodiment

In the description of the fourth embodiment, the base station AP2executes transmitter power control. In the fifth embodiment, a case willbe explained below wherein the base station AP2 controls the carriersense level.

In this case, the processes are basically the same as in the fourthembodiment. That is, the base station AP2 checks if the base station AP1executes directive beam control, on the basis of received power uponreceiving frame broadcasted from the base station AP1 and transmittingpower information of that received frame, and received power uponreceiving frame unicasted from the base station AP1 and transmittingpower information of that received frame. If it is determined that thedirective beam control is done, the base station AP2 may further checkif the degree of focus of directionality is enough to implement SDMA. Ifit is determined that the base station AP1 executes directive beamcontrol (with the degree of focus of directionality which is enough toimplement SDMA), the base station AP2 re-sets the carrier sense level ofthe self apparatus to increase it, thus adjusting to suppress thecarrier sense sensitivity to the minimum required level.

In such case, the base station AP2 may check if the base station AP1executes directive beam control, on the basis of received power uponreceiving frame broadcasted from the base station AP1, and that uponreceiving frame unicasted from the base station AP1, as in the fourthembodiment.

FIG. 24 shows an example of the arrangement of principal part of thebase station AP2 according to the fifth embodiment. The same referencenumerals in FIG. 24 denote the same parts as in FIG. 18, and onlydifferences will be explained. That is, in FIG. 24, a carrier sensecontrol unit 109 is added. As in the fourth embodiment, the base stationAP1 may have an adaptive array antenna, and may execute transmittingpower control as in the base station AP2 with the arrangement shown inFIG. 24. The following explanation will be given while taking the basestation AP2 as an example, but the same applies to the base station AP1.

When the beam gain estimating unit 105 determines that SDM can beimplemented, the carrier sense control unit 109 sets a high carriersense level in CSMA of the self apparatus within a range in which thecarrier sense function is effective, thus adjusting to suppress thecarrier sense sensitivity. Note that the circuit forincreasing/decreasing the carrier sense level is known to those who areskilled in the art.

The carrier sense level setting timing of the carrier sense control unit109 is the same as the transmitter power control of the fourthembodiment. That is, the carrier sense control unit 109 sets the carriersense level simultaneously with or in place of setting of transmittingpower in step S107 in FIG. 20, step S155 in FIG. 22, or step S162 inFIG. 23.

FIG. 25 is a flow chart for explaining the carrier sense level controlprocedure. Note that the same reference numerals denote the same stepsas in FIG. 21, and only differences will be mainly explained.

Steps S201 to S203 in FIG. 25 are the same as those in FIG. 21. That is,the beam gain estimating unit 105 checks in step S106 in FIG. 20, stepS154 in FIG. 22, or step S161 in FIG. 23 if the base station AP1executes directive beam control, on the basis of received power uponreceiving frame broadcasted from the base station AP1 and transmittingpower information of that received frame, and received power uponreceiving frame unicasted from the base station AP1 and transmittingpower information of that received frame (step S201), as has beenexplained in FIG. 21. If it is determined that the directive beamcontrol is executed, the beam gain estimating unit 105 further checks ifthe degree of focus of directionality in the base station AP1 is enoughto implement SDM (steps S202 and S203).

In FIG. 25 as well, whether or not the base station AP1 executesdirective beam control may be checked based on received power uponreceiving frame broadcasted from the base station AP1, and that uponreceiving frame unicasted from the base station AP1 without usingtransmitting power information, as described above.

For example, if the level of the gain of the directive beam is equal toor higher than a predetermined level, it is determined that SDMA can beimplemented (steps S201 to S203). As in the fourth embodiment, thechecking processes in steps S202 and S203 may be skipped. In such case,if it is determined in step S201 that the base station AP1 executesdirective beam control, the flow jumps to step S205 while skipping stepsS202 and S203.

If the beam gain estimating unit 105 determines in step S203 that SDMAcan be implemented, the carrier sense control unit 109 increases thecarrier sense level of the self apparatus by, e.g., a predeterminedlevel to suppress the carrier sense sensitivity (step S205). After that,carrier sense is done using the set carrier sense level.

As described above, according to the fifth embodiment, the base stationAP2 checks if the base station AP1 executes directive beam control, onthe basis of received power upon receiving a frame broadcasted from thebase station AP1, and that upon receiving a frame unicasted from thebase station AP1. If it is determined that the directive beam control isdone, the base station AP2 may further check if the degree of focus ofdirectionality is enough to implement SDMA. If it is determined that thebase station AP1 executes directive beam control (with the degree offocus of directionality which is enough to implement SDMA), the basestation AP2 increases the carrier sense level of the self apparatus (tominimize the carrier sense sensitivity). In this way, since the basestation AP2 minimizes the carrier sense sensitivity, it detects lessfrequently radio waves that the base station AP1 transmits incommunications with the terminals STA11 and STA12 in the first BSS orwith another base station. Therefore, when the base station AP2determines that no communication partner of the base station AP1 ispresent, it does not set the NAV (Network Allocation Vector) specifiedby IEEE802.11 (if the NAV is set, the base station AP2 waits access tothe base station AP1 for a period of time designated by the NAV). Hence,the base station AP2 can start transmission of frames to the basestation AP1.

Also, the base station AP2 may check if the base station AP1 executesdirective beam control, on the basis of received power upon receiving aframe broadcasted from the base station AP1 and transmitting powerinformation of that received frame, and received power upon receivingframe unicasted from the base station AP1 and transmitting powerinformation of that received frame. If it is determined that thedirective beam control is done, the base station AP2 may further checkif the degree of focus of directionality is enough to implement SDMA. Ifit is determined that the base station AP1 executes directive beamcontrol (with the degree of focus of directionality which is enough toimplement SDMA), the base station AP2 increases the carrier sense levelof the self apparatus (to minimize the carrier sense sensitivity). Inthis way, since the base station AP2 minimizes the carrier sensesensitivity, it detects less frequently radio waves that the basestation AP1 transmits in communications with the terminals STA11 andSTA12 in the first BSS or with another base station. Therefore, when thebase station AP2 determines that no communication partner of the basestation AP1 is present, it does not set the NAV (Network AllocationVector) specified by IEEE802.11 (if the NAV is set, the base station AP2waits access to the base station AP1 for a period of time designated bythe NAV). Hence, the base station AP2 can start transmission of framesto the base station AP1.

Note that the base station AP2 may have both the carrier sense controlunit 109 and transmitter power control unit 106 to control both thecarrier sense level and transmitting power, as shown in FIG. 24, or maycontrol one of the carrier sense level and transmitting power. Eithercase does not depart from the scope of the gist of the presentinvention.

The base station AP2 may have one of the carrier sense control unit 109and transmitter power control unit 106.

Sixth Embodiment

IEEE802.11 specifies an access control method, i.e., RTS/CTS. In thismethod, the right of transmission is assured using a control frame of aMAC frame shown in FIG. 6. Note that RTS/CTS control uses RTS and CTSframes, and an RTS or CTS frame can be identified by “type” and“subtype” in frame control in the MAC header.

This RTS/CTS control method can be applied to the wireless communicationsystem of FIG. 15. In such case, when the base station AP1 receives anRTS frame from the base station AP2, a CTS frame that the base stationAP1 returns to the base station AP2 as a response to the RTS frame istransmitted using a directive beam set toward the base station AP2. Inconsideration of this point, as in the fourth and fifth embodiments, thebase station AP2 controls the transmitting power and/or carrier senselevel on the basis of the transmitting power information and receivedpower of a received beacon frame, and those of the received CTS frame.Or alternatively, the base station AP2 controls the transmitting powerand/or carrier sense level on the basis of received power of a receivedbeacon frame, and that of the received CTS frame.

Since other arrangements are substantially the same as those in thefourth and fifth embodiments described above, the sixth embodiment willbe briefly explained below.

Upon generation of a transmission request, the base station AP2transmits an RTS frame to the base station AP1. In such case, iftransmitting power, which was set by the transmitter power control unit106 previously upon transmitting frame to the base station AP1, isavailable, the RTS frame is transmitted using that transmitting power.Otherwise, that frame may be transmitted with default transmittingpower.

Upon receiving the RTS frame, the base station AP1 sets a directive beamto be directed to the base station AP2 on the basis of the receivedpower at that time and the like. That is, the base station AP1 sets theaforementioned weighting factors corresponding to a direction in whichthe base station AP2 is present.

The base station AP1 transmits a CTS frame to the base station AP2 usingthe set directive beam. This CTS frame may contain transmitting powerinformation, as described above.

If the received frame type detection unit 103 determines that framereceived via the antenna is a CTS frame, the beam gain estimating unit105 receives the received power of that frame measured by the receivedpower measuring unit 102, and transmitting power information, which isextracted from that frame or is pre-stored in correspondence with theCTS frame, from the transmitted power detection unit 104.

At this time, the beam gain estimating unit 105 and transmitter powercontrol unit 106 execute the processes shown in FIG. 21 using thereceived power and transmitting power information of the CTS frame andthose of received beacon frame obtained in step S102 in FIG. 20, so asto set the transmitting power.

Or the processes shown in FIG. 25 are executed to set the carrier senselevel.

Or the transmitting power and carrier sense level may be set at the sametime.

In such case, the beam gain estimating unit 105 may receive only thereceived power of the frame measured by the received power measuringunit 102, and may set the transmitting power based on the receivedpower.

In the above description, the base station AP2 transmits an RTS frame tothe base station AP1. Also, in some cases, the base station AP1transmits an RTS frame to the base station AP2.

A case will be explained below wherein the base station AP1 transmits anRTS frame to the base station AP2.

In such case, if the base station AP1 already received frame transmittedfrom the base station AP2 as a communication partner previously, it setsa directive beam toward the base station AP2 based on the received powerat that time and the like, and transmits the RTS frame.

Hence, in consideration of this point, the base station AP2 may controlthe transmitting power and/or carrier sense level on the basis of thetransmitting power information and received power of the received beaconframe and those of the received RTS frame, as in the fourth and fifthembodiments.

That is, if the received frame type detection unit 103 determines thatframe received via the antenna 20, directional antenna 2, or adaptivearray antenna 25 is an RTS frame, the beam gain estimating unit 105receives the received power of that frame measured by the received powermeasuring unit 102, and transmitting power information, which isextracted from that frame or is pre-stored in correspondence with theRTS frame, from the transmitted power detection unit 104.

At this time, the beam gain estimating unit 105 and transmitter powercontrol unit 106 execute the processes shown in FIG. 21 using thereceived power and transmitting power information of the RTS frame andthose of received beacon frame obtained in step 5102 in FIG. 20, so asto set the transmitting power.

At the same time or in place of setting the transmitting power, theprocesses shown in FIG. 25 may be executed to set the carrier senselevel.

In such cases, the beam gain estimating unit 105 and transmitter powercontrol unit 106 may set the transmitting power using only the receivedpower measured upon receiving a beacon frame.

When the base station has executed the transmitter power control to setnew transmitting power, it transmits a CTS frame to the base station AP1using the set transmitting power.

Upon receiving the CTS frame, the base station AP1 re-sets a directivebeam toward the base station AP2 on the basis of the received power atthat time and the like, and uses that beam in subsequent communicationswith the base station AP2.

In this manner, the sixth embodiment can obtain the same effects as inthe fourth and fifth embodiments.

In the fourth to sixth embodiments, the base station AP2 can receivebeacon frames in any of the reception mode (step S2), authentication(step S4), association (step S5), communications (step SE),disassociation (step S8), and deauthentication (step S9) in FIG. 19 inprinciple. Hence, if the base station AP2 receives a frame addressed(unicasted) to the self apparatus after it receives a beacon frame, itcan execute transmitter power control and carrier sense level controlshown in FIGS. 21 and 25 anytime.

In the first to fifth embodiments, communication between two basestations have been explained. Also, three or more base stations can beconnected wirelessly using the above method. Especially, when each basestation has a directional antenna, a plurality of base stations can beconnected not only in series but in a tree-, ring-, and mesh-patterns.

In this way, not only one but also a plurality of new base stations tobe connected wirelessly can be set, and prompt actions can be taken onbroadening the communication area, and on an improvement ofcommunication quality with a terminal apparatus in a very bad wirelesscommunication environment.

The first to sixth embodiments can be combined as needed.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A wireless communication apparatus having a relay function,configured for: (a) receiving a beacon frame transmitted from anotherwireless communication apparatus having a relay function; (b)transmitting, to the another wireless communication apparatus, anauthentication request frame used in an authentication process; (c)receiving an authentication response frame used in the authenticationprocess and transmitted from the another wireless communicationapparatus; (d) transmitting, to the another wireless communicationapparatus, an association request frame used in an association process;(e) receiving an association response frame used in the associationprocess and transmitted from the another wireless communicationapparatus; and (f) associating with the another wireless communicationapparatus if the authentication process and the association processsucceed; the wireless communication apparatus comprising: a unitconfigured to insert a data item into one or more fields which areincluded in at least one of the authentication request frame and theassociation request frame, the data item indicating the wirelesscommunication apparatus has a relay function; and a transmitter unitconfigured to transmit at least one of the authentication request frameand the association request frame including the data item, in theauthentication process and/or association process.
 2. The wirelesscommunication apparatus according to claim 1, wherein the wirelesscommunication apparatus is configured for communicating with the anotherwireless communication apparatus and terminals arranged to associatewith the wireless communication apparatus using a same channel.
 3. Thewireless communication apparatus according to claim 1, furthercomprising: a receiver unit configured to receive a first address tablecontaining addresses of terminals arranged to associate with the anotherwireless communication apparatus.
 4. The wireless communicationapparatus according to claim 3, further comprising: a unit configured torelay a data frame addressed to a terminal arranged to associate withthe another wireless communication apparatus by using the first addresstable.
 5. The wireless communication apparatus according to claim 1,further comprising: a second transmitter unit configured to transmit, tothe another wireless communication apparatus, a second address tablecontaining addresses of terminals arranged to associate with thewireless communication apparatus.
 6. The wireless communicationapparatus according to claim 1, further comprising: a second receiverunit configured to receive a frame of a plurality of frames including(a) a first frame transmitted from a terminal arranged to associate withthe wireless communication apparatus, (b) a second frame used incommunication among the another wireless communication apparatus andterminals arranged to associate with the another wireless communicationapparatus, and (c) a third frame used in communication among theterminals arranged to associate with the another wireless communicationapparatuses; and a transmission controlling unit configured (a) tosuppress, when the frame received is the first frame, transmission offrames with respect to the another wireless communication apparatus andframes with respect to terminals arranged to associate with the wirelesscommunication apparatus, and (b) not to suppress the transmission whenthe frame received is the second or the third frame.
 7. A terminalarranged to associate with the apparatus according to claim 1,comprising: a receiver unit configured to receive a frame of a pluralityof frames including (a) a first frame which is not addressed to theterminal and is transmitted from the wireless communication apparatus oranother terminal arranged to associate with the wireless communicationapparatus, (b) a second frame used in communication among the anotherwireless communication apparatus and terminals arranged to associatewith the another wireless communication apparatus, and (c) a third frameused in communication among the terminals arranged to associate with theanother wireless communication apparatuses; and a transmissioncontrolling unit configured (a) to suppress transmission of frames whenthe frame received is the first frame, and (b) not to suppress thetransmission when the frame received is the second or the third frame.8. The wireless communication apparatus according to claim 6, whereinthe transmission controlling unit suppresses the transmission for apredetermined time.
 9. The wireless communication apparatus according toclaim 1, further comprising: an antenna; and a receiver unit configuredto receive the beacon frame, the authentication response frame, and theassociation response frame through the antenna, wherein the transmitterunit is configured to transmit the authentication request frame and theassociation request frame through the antenna.
 10. A wirelesscommunication apparatus having a relay function, configured for: (a)receiving a beacon frame transmitted from another wireless communicationapparatus having a relay function; (b) transmitting, to the anotherwireless communication apparatus, an authentication request frame usedin an authentication process; (c) receiving an authentication responseframe used in the authentication process and transmitted from theanother wireless communication apparatus; (d) transmitting, to theanother wireless communication apparatus, an association request frameused in an association process; (e) receiving an association responseframe used in the association process and transmitted from the anotherwireless communication apparatus; and (f) associating with the anotherwireless communication apparatus if the authentication process and theassociation process succeed; the wireless communication apparatuscomprising: a unit configured to insert a data item into one or morefields which are included in a frame used in at least one of theauthentication process and association process, the data item indicatingthe wireless communication apparatus has a relay function; and atransmitter unit configured to transmit the frame including the dataitem, in the authentication process or association process.
 11. Thewireless communication apparatus according to claim 10, furthercomprising: an antenna; and a receiver unit configured to receive thebeacon frame, the authentication response frame, and the associationresponse frame through the antenna, wherein the transmitter unit isconfigured to transmit the authentication request frame, the associationrequest frame, and the frame including the data item through theantenna.